1. Field of Invention
The present invention relates to heat exchangers for gas and wood fireplaces, and, in particular, it embraces the obstruction of a flow of flue gas by a thin walled air conduit. The obstruction increases the amount of time in which the hot flue gas contacts the air conduit and increases the heat transfer surface area.
2. Description of Related Art
Fireplace heat exchangers are well known. However, the amount of time in which the hot flue gas is in contact with the heat transfer surface area (and the quantity of heat transferred) is generally limited. Accordingly, the amount of heat transfer is limited as is the heating capacity of the fireplace unit.
U.S. Pat. No. 4,878,478 to Johnson discloses the use of a heat exchange chamber for circling air about an inner shell to heat the circulated air. Johnson further teaches the use of fans to aid in the flow of air. The heat exchange chamber comprises a passageway which surrounds a wood fire within the fire chamber. However, such a heat exchange chamber suffers from several significant shortcomings and drawbacks. In particular, this prior art heat exchange chamber is not insertable into a standard fireplace unit. Also, the heat exchange surface area is limited as is the time in which the hot flue gases contact the surface which transfers heat into the air to be heated.
U.S. Pat. No. 4,854,298 to Craver discloses a wood burning stove having a lower conduit, a vertical rear conduit and an upper conduit. Ambient air enters the lower conduit and receives heat from the floor of the combustion chamber. The heated air is transferred from the rear conduit to an upper bonnet. The upper bonnet has two diverging side walls which direct the heated air through two forward facing outlets. A fan is used to aid in the flow of air through the conduit. However, such a heat exchange chamber suffers from several significant shortcomings and drawbacks. In particular, the heat exchange surface area is limited as is the time in which the hot flue gases contact the surface which transfers heat into the air to be heated. Also, this prior art heat exchange chamber is not insertable into a conventional fireplace unit.
U.S. Pat. No. 4,665,890 to Drewsen discloses a fireplace insert which routes smoke, created in the process of burning, through a smoke duct work. Heat is transferred from the duct work directly to the outside of the fireplace unit. Heat is also transferred to ambient air within an air duct. The air duct follows the sides and back of the firebox. Such a heat exchange chamber suffers from several significant shortcomings and drawbacks. In particular, this prior art heat exchange chamber is not insertable into a conventional fireplace unit. Also, the heat exchange surface area is not maximized. Further, the time in which the hot flue gases contact the surface which transfers heat into the air to be heated is not maximized.
U.S. Pat. No. 4,558,688 to Piazzetta discloses a fireplace-heater having air inlet grids at the top of the fireplace heater. The air inlet grids lead to two vertical chambers which follow the vertical portion of the burner unit. The vertical chambers lead to an intake chamber. The intake chamber is connected to the suction side of a ventilating unit. The delivery side of the ventilating unit opens, through flexible hoses, to grids located in the lower portion of the heater. The grids discharge heated air. The vertical chambers encompass two pairs of chambers. The chambers connect to form a U-shape. Hot flue gas travels upward and enters the aforementioned chambers. The hot flue gas travels down the chambers and is routed upwardly to a second chamber to be discharged through a chimney union. However, such a heat exchange chamber suffers from several significant shortcomings and drawbacks. In particular, this prior art heat exchange chamber is not insertable into a standard fireplace unit and it must follow the vertical portion of the burner.
U.S. Pat. No. 4,519,376 to Schoeff, et al. discloses a heat exchanger which divides a flow of air to be heated. One portion of the air passes through primary heat transfer surfaces and secondary heat transfer surfaces. Another portion passes between secondary heat transfer surfaces and the outer walls. The secondary heat transfer surface is heated by direct radiation from primary heat transfer surfaces which in turn heats the air there between. Thereafter, the heated secondary heat transfer surface heats the outer walls which in turn transfers the heat energy to the air passing there between. These heat transfer surfaces follow the lower back and top portions of the fireplace assembly. The unit is not insertable into a standard fireplace unit.
U.S. Pat. No. 4,515,145 to Tallman et al. discloses a gas-fire condensing mode furnace having a heat exchanger. The heat exchanger is located in the air passage and transfers heat, from the products of combustion, to an air passage. The heat exchanger comprises an elongated conduit having a serpentine configuration with its intake end communicating with the gas burner enclosure. Air to be heated is drawn into an air passage by means of a blower and is caused to flow over the heat exchanger. Heat is extracted from the heat exchanger and the hot air is discharged through a hot air discharge duct located at the top of the furnace. Tallman et al. is not directed toward fireplace inserts. Further, such a heat exchange chamber suffers from several significant shortcomings and drawbacks. In particular, it is very bulky and is not insertable into a conventional fireplace unit.
U.S. Pat. No. 4,206,743 to Niemeia discloses a heating apparatus wherein the combustion chamber is at least partially surrounded by an air heating enclosure through which ambient air is forced by a fan for heating. Ambient heated air released through a heated air outlet located at the top of the stove. The ambient air is drawn into the heating enclosure through a lower portion of the unit. Niemeia does not relate to a fireplace insert. Further, such a heat exchange chamber suffers from several significant shortcomings and drawbacks. In particular, this prior art heat exchange chamber is not insertable into a conventional fireplace unit and is very bulky.
U.S. Pat. No. 4,200,086 to Kolb discloses an air to air heat exchanger insert for use in a wood burning stove or fireplace. The heat exchanger insert includes two chambers separated by a baffle plate. The baffle plate extends over a major portion of the length of the heat exchanger insert. The baffle plate forms a "U" shaped circulation pattern. Hot air travels under, around and over the insert and out through the flue connection. However, such a heat exchanger suffers from several significant shortcomings and drawbacks. In particular, this prior art heat exchanger requires the use of baffle plates which increases the number of steps in the manufacturing process.
Accordingly, none of the related art describes a parallel flow heat exchanger having a thin walled chamber, with a thin walled air conduit extending therethrough, a port for the introduction of hot flue gas and a port for the release of flue gas.
Nor does any of the related art describe a sinusoidal passageway embodiment, wherein ambient air from a lower air conduit of the heat exchanger is passed to a middle air conduit and then transferred to an upper air conduit for further heating and discharged into an area to be heated
It is therefore an object of the present invention to provide a heat exchanger with a low air pressure drop and a high heat exchange.
It is a further object of the further invention to provide a more efficient heat exchanger for gas and wood fireplaces.
It is yet another object of the present invention to provide a heat exchanger which cools a portion of the fireplace.
It is an additional object of the present invention to provide a non-bulky heat exchanger which may be inserted into conventional gas and wood burning fireplaces.